Thin glass sheets have found use in many optical, electronic or optoeletronic devices, such as liquid crystal displays (LCD), organic light-emitting diode (OLED) displays, solar cells, as semiconductor device substrates, color filter substrates, cover sheets, and the like. The thin glass sheets, having a thickness from several micrometers to several millimeters, may be fabricated by a number of methods, such as float process, fusion down-draw process (a method pioneered by Corning Incorporated, Corning, N.Y., U.S.A.), slot down-draw process, and the like.
In many of the applications of thin glass sheets, it is highly desired that the glass sheets have (i) pristine surface quality essentially free of scratches, particles, and other defects; (ii) high thickness uniformity; (iii) low surface roughness and waviness. To that end, in the forming process for making the glass sheets, typically direct contact of the center region of major surfaces of the as-formed glass sheet with solid surfaces is avoided. Instead, only the peripheral region of the glass sheet was subjected to direct contact with solid surfaces such as edge rolls, pulling rolls, edge guiding rolls, and the like. Thus, the peripheral portions of both sides of an as-formed glass sheet obtained directly from the forming device, such as in the bottom-of-draw area of a fusion down-draw or slot down-draw process, sometimes called “beads,” tend to have lower surface quality than the center region of the major surfaces. In addition, depending on the specific forming device used, the peripheral portions tend to have different thickness and significantly higher thickness variation than the center region.
Various glass sheet bead removal technologies were used or proposed previously with a different yield, yield consistency, and cost of the processes and equipment.
The display market has shown increasing demand for glass sheets with high flexibility, i.e., those with large sheet width and/or length, and/or very small thickness. The present inventors have found that, for glass sheets with high flexibility, bead removal can be a significant challenge and an overall yield bottleneck in a glass sheet manufacture process. Thus, an acceptable bead removal process for a glass sheet with relatively low flexibility may be unacceptable for a glass sheet with significantly higher flexibility.
Thus, there is a genuine need of a robust glass sheet bead removal process with acceptable capability for glass sheets with high and/or low flexibility. The present invention satisfies this and other needs.